This invention relates to a grooved spherical bearing for vertical machines (particularly those whose number of revolutions is in a range between 20,000 and 50,000 r.p.m.) which is adapted to increase the quantity of lubricating oil circulating past the sliding surfaces of the bearing.
A grooved spherical bearing for bearing a vertical machine is characterized by being able to simultaneously bear both thrust and radial loads, having a high loading capacity, and being relatively low in bearing loss. Because of this characterizing features, it is used as a bearing device for a high-speed rotary machine, e.g. a centrifugal separator.
This type of bearing consists of a pivot or a rotatable member having a spherical end portion, and a cup bearing element or a stationary member concentric with the pivot and semi-spherically or hemi-spherically concave in shape, with a gap being formed between the rotatable member and the stationary member. The cup bearing element and the spherical end portion of the pivot are immersed in lubricating oil contained in an oil tank, and a plurality of grooves formed on the surface of the spherical end portion of the pivot disposed in spaced juxtaposed relation to the cup bearing element are arranged on the entire surface of the spherical end portion in such a manner that the grooves perform the function of the blades of a pump as the pivot rotates. Thus, when the pivot rotates, the pooled oil in the oil tank is drawn through the intake (the end of each groove remote from the end of the spherical end portion) into the gap by the pumping action of the grooves, so that the pressure of the oil film formed in the gap by the lubricating oil is increased in supporting the bearing load.
This type of bearing has oil film characteristics which vary from those of other types of bearing in that the thickness of the oil film increases with an increase in the number of revolutions, is maximized when the number of revolutions reaches a certain level, and rapidly decreases after the number of revolutions exceeds this level. It is empirically known that, because of these characteristics, the temperature of the bearing rapidly rises and the bearing becomes unfit for use when the number of revolutions exceeds a certain level, in case the bearing is used with a machine rotating at high speeds, e.g. a centrifugal separator handling gases. It has in the past been believed that this phenomenon is due to a lowering in the viscosity of the lubricating oil caused by an increase in bearing load. Attempts have been made, therefore, to effect cooling of the bearing so as to avoid a lowering in the viscosity of lubricating oil. However, no satisfactory results have been achieved by these attempts.
Inventors have conducted research into the behavior of the pooled oil disposed in the vicinity of the intake of each groove of this type of bearing when the shaft supported by the bearing rotates at high speeds. The results show that the lubricating oil in this region is caused by the force of inertia to flow in a radial direction and that this stream of lubricating oil prevents the pooled oil from being drawn through the intake of each groove into the gap. Thus it has been ascertained that the formation of the radial flow of the oil prevents the oil from being drawn into the gap and causes a reduction in the thickness of the oil film, thereby resulting in a sudden rise in the temperature of the bearing. Unless operation of the machine is interrupted at this stage, the bearing will develop seizure, making further operation of the machine impossible.